Thymops

Thymops birsteini is a species of decapods from the family of lobster -like. The Hummerart described in 1972 is used in the deep sea of the South Atlantic in Argentina and Chile.

Description

The rostrum of Thymops birsteini is narrow and extends far beyond the antenna bases ( antennal peduncles ). It has lateral, but not belly or back side spines. The surface of the rostrum has a center recess, which continues as a flat line in the longitudinal direction over the whole carapace. As with the type Thymopsis nilenta located approximately from the middle of the rostrum two parallel to the recess extending ridges, which are provided with seven or eight sharp tips.

The slightly hairy carapace is generally irregularly finely granulated. The individual segments ( somites ) of Pleons have a transverse recess. The telson is distinctly longer than wide and longer than the sixth Thus. The back -side surface of the telson is granulated and has two blunt and rather inconspicuous ridges. The eyes are rather small, reduced and not pigmented, but movable. The exopodite of the antenna ( Scaphocerite ) is missing. The exopodite of the second maxillipeds is reduced and without flagellum, the third is very small.

The large claws on the first pair of walking legs are the same, relatively large and covered with many spines or nodules. The scissor fingers are about as long as the scissors hand. The scissors finger pointed towards the end too, are bent inward and cross over each other when closing the scissors. On the second and third pair of walking legs are very small scissors, the fourth and fifth is scherenlos. Very occasionally the second and third pair are provided with hair.

In males, the segments of the first pair of legs are floating motionless merged, the endo-and Exopoditen the second to fifth swimming leg pairs are relatively slim. On the endopodite of the second pair is the "Appendix masculina ", a type clamp-like attachment, relatively short. In females, the first pair consists of two movable segments, the location on the body ( basal ) is shorter. The remaining swimming legs of the females resemble those of the third to fifth pair of the male.

The uropods are relatively wide and have a running lengthwise in the middle ridge, the outer edge of the endopodite ends in a single peak. The exopodite has a distinct diaeresis, a transverse depression which carries out about 20 small tips forward.

Males and females have approximately the same body size. Maximum is probably a carapace length of about 13 cm and a weight of 300 g thereby attained the smallest mature female had a carapace length of 3 cm. Females with freshly spawned eggs were caught both in spring and autumn. The largest number of eggs a female was 378, the number of eggs correlated with body size. Eggs are initially yellowish- orange and have sizes of up to 2 mm. The eggs are about 3 mm long and yellowish brown just before hatching. At hatching, the larvae have a carapace length of about 2 mm. Unlike other lobsters, whose larvae go directly to a planktonic lifestyle, newly hatched larvae are initially still attached to the swimming legs of the females.

Distribution and habitat

Thymops birsteini is in the continental shelf and the deep sea on the coasts of Argentina, Uruguay and Chile, and to the north, east and southeast of the Falkland Islands and east of South Georgia native. The distribution area is located in the Pacific Ocean south of 51 ° S and in the Atlantic Ocean south of 37 ° S to a maximum of 57 ° S. The water depths ranging from 175 m in this case up to a maximum 1662 m, where the vast majority of catches from depths between 1000 m and 1400 m come.

Due to its large distribution area Thymops birsteini is "not endangered" ( Least concern ). In addition, this species is so far fished as bycatch, although it could be of commercial interest.

The habitat is characterized by soft mud where Thymops birsteini daytime staying in self-dug caves. Enemies of this Hummerart are, inter alia, Patagonian toothfish ( Dissostichus eleginoides ), grenadier fish of the genus Macrourus and the Kalmar Onykia ingens.

Systematics and Taxonomy

The first description of Thymops birsteini was carried out by Russian scientists NA Zarenkov and VN Semenov as Nephropides birsteini. Lipke Holthuis presented with this single species the genus Thymops on and incorporated it together with the newly described genus Thymopsis Holthuis, 1974 in a separate subfamily within the lobster -like, the Thymopinae Holthuis, 1974. However, results support a phylogenetic investigation, no subdivision of the family of lobster -like in sub-families, which is why they are no longer in use. Shane Ahyong and coauthors described in 2012 the kind Thymops takedai, the genus is therefore no longer monotypic. Thymops birsteini, unlike Thymops takedai a ventral side straight rostrum, the Exopoditen of the third maxillipeds have flagella and the carapace has a different ornamentation.

From the closely related genus Thymopsis to Thymops differs mainly by the presence of Exopoditen to the second and third maxillipeds. Together with the Kaphummer ( Homarinus capensis ) and the genus Thymopides forms Thymops a clade within the lobster -like.